Implantable hemodynamic monitors are available for monitoring right ventricular pressure chronically in an ambulatory patient. Patients with congestive heart failure (CHF) have elevated cardiac filling pressures and reduced cardiac output. A major treatment objective is to lower filling pressures while maintaining adequate cardiac output. Therefore, from a hemodynamic monitoring perspective, it is advantageous to monitor both filling pressures and measures of cardiac output.
Chronic pressure monitoring in ambulatory patients using chronically implantable pressure sensors has been realized. However, direct monitoring of flow chronically in an ambulatory patient has not been realized clinically. Pressure measurements alone do not account for variations in vascular impedance, which changes in response to varying physiological conditions and is time-varying over the cardiac cycle. Variations in vascular impedance will affect the forward arterial flow produced by developed pressure in the ventricles. Pressure pulse contour cardiac output methods have been developed for estimating flow from arterial pressure signals, however, such methods generally require frequent calibration, particularly after a suspected change in hemodynamics.